In the microfabrication using a resist composition, with an increase in the integration degree of an integrated circuit, formation of an ultrafine pattern is required. To meet this requirement, the exposure wavelength tends to become shorter, such as from g line to i line or further to excimer laser light, and, for example, development of a lithography technique using an electron beam is proceeding. As the resin used for the exposure to excimer laser light such as KrF excimer laser, a resin having a structure where a hydrogen atom of a phenolic hydroxyl group is replaced by a group having an aliphatic hydrocarbon residue, a resin having a structure where the hydrogen atom is replaced by a group having an aryl group, and a resin having a structure where the hydrogen atom is replaced by an alkyl group, are described in JP-A-2000-29220 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”), Japanese Patent No. 3,546,687 and JP-A-7-295220, respectively.
In order to form an ultrafine pattern, thin film formation of the resist is necessary, but when the resist is formed as a thin film, its dry etching resistance is reduced. Also, in the electron beam lithography, recently, the accelerating voltage of the electron beam (EB) is increased to reduce the effect of electron scattering (forward scattering) in the resist film. However, in this case, the resist film is reduced in the electron energy trapping ratio to decrease the sensitivity, and the effect of scattering (back scattering) of electrons reflected in the resist substrate increases. In particular, when forming an isolated pattern having a large exposure area, the effect of back scattering is large, and the resolution of the isolated pattern is impaired.
Particularly, in the case of patterning on a photomask blanks used for semiconductor exposure, a light-shielding film containing a heavy atom is present as the layer below the resist, and the effect of backward scattering attributable to the heavy atom is serious. Therefore, in the case of forming an isolated pattern on a photomask blanks, among others, the resolution is highly likely to decrease.
As one of the methods to solve these problems, use of a resin having a polycyclic aromatic skeleton such as naphthalene is being studied (see, for example, JP-A-2008-95009 and JP-A-2009-86354), but the problem about the resolution of an isolated pattern has been unsolved. In JP-A-2005-99558, as one of the methods to enhance the resolution of an isolated pattern, a resin containing a group for adjusting the solubility is used, but it has not been achieved to sufficiently satisfy the resolution of an isolated pattern.
Also, the microfabrication using a resist composition is not only used directly to produce an integrated circuit but also applied, in recent year, to the fabrication or the like of a so-called imprint mold structure (see, for example, JP-A-2008-162101 and Yoshihiko Hirai (compiler), Nanoimprint no Kiso to Gijutsu Kaihatsu●Oyo Tenkai-Nanoimprint no Kiban Gijutsu to Saishin no Gijutsu Tenkai (Basic and Technology Expansion●Application Development of Nanoimprint-Fundamental Technology of Nanoimprint and Latest Technology Expansion), Frontier Shuppan (issued June, 2006)). Therefore, it becomes an important task to satisfy high sensitivity, high resolution property (for example, high resolution, excellent pattern profile and small line edge roughness (LER)) and good dry etching resistance all at the same time, and this needs to be solved.